Field of the Invention
The invention relates to a spectrometer with monochromator and order sorting filter for absorption spectrometry on samples in microplate wells, as well as a scanning method for detecting the absorption spectrum of samples in microplate wells, in which a spectrometer equipped with a monochromator and such an order sorting filter is used.
Spectrometers with monochromator have been known for a longer period of time and are used for example for generating illumination light of a specific wavelength for the examination of the absorption characteristics of clear low-molecular solutions. Spectrometers are also used for detecting and measuring light over a wide wavelength range, which comprises the near infrared light, the visible light and the ultraviolet light of the electromagnetic spectrum.
Description of Related Art
A special rapid scanning spectrophotometer is known from U.S. Pat. No. 4,225,233, which produces illumination light with a predetermined wavelength depending on control voltage signals emitted to a scanning element. A scanning element, which in contrast to conventional spectrometers is arranged in the grating image plane of the spectrophotometer, is formed as a small mirror which is fixed to the rotor of a galvanometer. The angular position of said galvanometer is precisely controlled by a closed-loop electronic control circuit. The light spectrum reflected by the mirror is guided through a slit, thus providing light with the predetermined wavelength in a range of 50 to 300 nm or even 50 to 600 nm. The wavelength range is linearly scanned. A reduced wavelength precision must be accepted however in the higher wavelength range due to the limitation of the drive of the galvanometer.
In contrast to the generation of an illumination beam by a mirror for deflecting the spectrum provided by a monochromator for examining a sample, an order sorting filter (OSF) is provided downstream of the used dispersion grating in patent U.S. Pat. No. 7,924,422 B2 during the spectrometric detection of the light reflected from an examined object. This document discloses a calibration method for optical metrology. The illustrated OSF comprises three filtering zones, but it can also comprise fewer or more filtering zones. Each of the exemplary three filtering zones acts as a long-pass or bandpass filter in order to prevent that the pixels of the array detector (e.g. a CCD or CMOS sensor) situated directly beneath receive light of orders of diffraction which are higher than the measured orders of diffraction (typically one of the first orders +/−1). The disclosed OSF can be used for a wavelength range which reaches from near infrared light (NIR) via the visible light (VIS) and ultraviolet light (UV) up to deep ultraviolet light (DUV) of the electromagnetic spectrum. Order sorting filters with three zones are known from patent U.S. Pat. No. 7,924,422 B2, whose transmission range is produced by thin-film filter stacks which are all arranged on a common, optically transparent substrate and at least partly on bottom layers. The drawings show in FIG. 1A an order sorting filter with mutually abutting thin-film filter stacks (cf. FIG. 8 of U.S. Pat. No. 7,924,422 B2) and in FIG. 1B an order sorting filter with mutually partly overlapping thin-film filter stacks (cf. FIG. 9 of U.S. Pat. No. 7,924,422 B2).
Document U.S. Pat. No. 3,711,708 discloses a rapid scanner for detecting infrared spectrums at the output of a gas chromatograph, document EP 0 015 607 A1 discloses a modified Ebert monochromator for a spectrometer, and document WO 93/22636 A1 discloses a monochromator arranged on a separate housing and comprising one respective fixed inlet and outlet gap, a diffraction grating and an edge filter which is continuously driven by a grating drive and with angular synchronism in relation to the grating.
Document U.S. Pat. No. 6,313,471 B1 discloses a device for determining fluorescence, luminescence or absorption of a sample which is situated in a cuvette or in a well of a microplate. The device comprises a broadband light source, a monochromator arranged in a separate housing, and a filter wheel with a number of separate bandpass and/or edge filters for controlling the wavelength of the light impinging on the detector. The excitation light and the emission light are brought in one optical fibre each close to the sample in a well or close to the detector.